It is known to pass photosensitive sheet material, after exposure in a suitable device, through a developing unit in which the photosensitive surface is treated with a gaseous or vapor medium for so-called dry development.
In blueprint-making processes and the like, for example, the blueprint after exposure can be transported through a housing of the developer unit by appropriate transport rollers and there contacted with ammonia vapors or some other developing agent in a gaseous state.
Because of the noisome or toxic nature of the vapor or gaseous medium it is known to provide locks or shielding chambers at the inlet and outlet sides of the developing chamber to prevent or limit the escape of the gas or vapor to the environment. In German patent documents (Auslegeschrift) DE-AS No. 25 23 228 and DE-AS No. 27 26 240, for example, apparatus for the dry development of blueprints of the aforedescribed type is described. In these systems both the incoming and outgoing shielding chambers are provided with pairs of rollers which act in part as transport rollers for the sheet material and in part as a barrier to escape of any gaseous or vapor medium into the ambient atmosphere. A second pair of rollers is disposed between each shielding chamber and the developing chamber to seal the latter, to a certain degree, against excessive transfer of the gas or vapor from the developing chamber to the respective shielding chamber.
However, during operation of the developing unit, the pairs of rollers are continuously driven as is unavoidable if they are to function at least in part as the transport means for the paper. It has been found that portions of the gaseous or vapor developing medium tend to deposit upon and accumulate by adhesion upon these rollers so that it is unavoidable that at least to a certain extent the developing medium is carried by the outer pairs of rollers into the ambient atmosphere. The result is a noisome odor in the region of the device and possibly a toxic condition.